Railway Science (Chemistry-Acid ,Bases and Salt) (Part-II)

(Sodium Hydroxide) - It is a crystalline solid, colorless in nature. This compound is highly water-soluble and consists of sodium cations and hydroxide anions. It absorbs moisture from the air. Bases - It can be defined as substances that produce hydroxide ions when dissolved in water (OH⁻). Acid - a substance or compound that releases hydrogen ions (H⁺) when in solution.

The most common tests for acid and bases are litmus paper tests. Blue litmus turns red for acidic solution and red litmus turns blue for a basic solution. pH scale is also a method for testing the acidic, basic and neutral nature of a solution.

Phenolphthalein is often used as an Indicator in Acid-Base titrations. It is colorless in acid. Formula: C₂₀H₁₄O₄ . Its structure has three hexagonal and one pentagonal structures, two alcoholic groups, and one ketone group. Ionization is responsible for the color change of the compound (Phenolphthalein).

Example: H₂O, Pyridine and its derivatives. Lewis-acid: A substance that has empty orbitals and can accept a pair of electrons. Examples: Copper (Cu), H⁺  ions along with H₃O⁺ . Bronsted-Lowry Acid: A substance that donates a proton H⁺ ion to another compound. Acid ⇌ Proton + Conjugate Base (A conjugate base can accept a proton and acid reforms). Bronsted-Lowry Base: A substance that accepts a proton or H⁺ ion from other compounds. Base + Proton ⇌ Conjugate Acid (A conjugate acid can donate a proton and base reforms).

Acid - base reaction taking place to form Sodium Carbonate (Na₂CO₃) is given as: H₂CO₃ + 2NaOH → Na₂CO₃+ 2H₂O. Carbonic acid (H₂CO₃) is a weak acid, and sodium hydroxide (NaOH) is a strong base. When sodium carbonate dissolves in water, it dissociates into sodium ions (Na⁺) and carbonate ions (CO₃)²⁻ . The carbonate ions can accept protons from water to form bicarbonate ions (HCO₃⁻) and hydroxide ions (OH⁻), increasing the pH of the solution and making it basic.

Universal indicator:- It is a mixture of several indicators that shows a colour change in a solution, indicating the acidity or alkalinity of solutions. Some common universal indicators : Litmus (turns red in acidic solutions and blue in basic solutions), Phenolphthalein (colourless in acidic solutions and turns pink in basic solutions), Methyl red (turns red in acidic solutions and yellow in basic solutions), Bromothymol blue (turns yellow in acidic solutions, green in neutral solutions, and blue in basic solutions).

It is a water soluble mixture of coloured organic compounds obtained from several species of lichens. It is used to produce the pH indicator to determine whether a solution is acidic or basic. In an acidic medium, blue litmus paper turns red and in a basic or alkaline medium, red litmus paper turns blue.

Ammonium chloride (NH₄Cl) is a white crystalline salt that is highly soluble in water. Uses: fertilizers as a nitrogen source, electrolyte in dry cells, medicine (cough syrups) as an expectorant.

Tartaric acid. Uses of Baking Powder - Lightening the texture and increasing the volume of various baked foods. Tartaric acid (C₄H₆O₆): It is a natural component found in fruits and vegetables such as grapes, tomatoes, and bananas.

Hydrochloric acid (HCl) is an inorganic chemical and a strong corrosive acid (pH : 2). Uses - In rubber industries, textile industries, to regulate the PH of solutions. Sodium hydroxide (caustic soda) is a white, translucent crystalline solid. It does not occur naturally. Uses - In the manufacturing of detergents and soaps; to prevent bacteria and mold growth; in papermaking.